The field of the invention is a process and apparatus for the removal of elements from water, and more particularly the removal of contaminants, such as selenium.
Selenium is a naturally occurring metalloid element having atomic number 34 and an atomic weight of 78.96. Selenium is widely dispersed in igneous rock. Selenium also appears in large quantities, but in low concentrations, in sulfide and porphyry copper deposits. Moreover selenium is widely associated with various types of sedimentary rock. Inorganic selenium is most commonly found in four oxidation states (Se6+, Se4+, Se0, and Se2−). Selenate (SeO42−, Se(VI)) and selenite (SeO32−, Se(IV)) are highly water soluble. Elemental selenium (Se0) is insoluble in water.
Selenium is a common water contaminant throughout the United States and the world and represents a major environmental problem. Human related selenium release originates from many sources including mining operations, mineral processing, abandoned mine sites, petroleum processing, and agricultural run-off. The principal sources of selenium in mining are copper and uranium bearing ores and sulfur deposits. Selenium is commonly found in these mining wastewaters in concentrations ranging from a few micrograms per liter up to more than 12 mg/L. In precious metals operations, waste and process water and heap leachate solutions may contain selenium at concentrations up to 30 mg/L. It has been observed that concentrations of selenate as low as 10 μg/L in water can cause death and birth deformities in waterfowl; therefore, the established regulatory limit is 5 μg/L. Most of these mining operations, including both metal and non-metal mining operations, will need inexpensive and effective selenium removal processes to meet discharge and closure requirements. Additionally, the selenium removal difficulties include the different dissolved species, no direct precipitation chemistries, difficulty of reducing selenate, and sulfate interference.
The present invention attempts to solve these problems, as well as others.